Retention mechanisms Dotaz Zobrazit nápovědu
In the scope of the present review, the current status of high-performance liquid chromatography/ultra-high performance liquid chromatography and supercritical fluid chromatography is briefly provided. These techniques and their retention mechanisms are compared. Various alternative approaches utilized for the determination and description of the retention processes in these two systems are mapped. Two frequently used concepts, linear-free energy relationships, and hydrophobic subtraction models, used for the characterization of the retention interactions, are discussed. Principles and selected applications of the both methods are also covered. Then the models applied for the prediction of retention behavior of solutes on stationary phases are outlined. The procedures utilized for the sorbent/column classification are also covered. Simple chromatographic tests frequently used for the basic characterization and mutual comparison of stationary phases are summarized and briefly commented on. The importance of a statistical evaluation of complex retention data obtained from the chromatographic measurements is outlined. Finally, computer simulations aiming at the facilitation of the quest to optimize separation conditions for a given mixture of analytes are touched upon.
- Klíčová slova
- Characterization, Retention mechanisms, Retention models, Stationary phases,
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
The influence of the mobile phase and temperature, on the retention behavior of seven aliphatic acids (pyruvic, gluconic, 2-oxoglutaric, tartaric, malic, oxalic, and citric acid) in hydrophilic interaction liquid chromatography on zwitterionic stationary phases with sulfobetaine and phosphorylcholine ligands is investigated. In agreement with the van't Hoff model, most acids show linear ln k versus 1/T plots. However, the retention of structurally symmetrical oxalic and tartaric dicarboxylic acids is almost independent of temperature, or slightly increases at rising temperature. The experimental parameters of the van't Hoff plots suggest positive entropic contributions to the retention of these symmetrical acids, possibly connected with changes in molecular symmetry on their adsorption. The type of the zwitterionic stationary phase and the mobile phase composition (the molar concentration of acetate buffer and the volume fraction of acetonitrile) affect the retention and the selectivity of the separation of the acids.
- Klíčová slova
- Aliphatic carboxylic acids, Hydrophilic interaction chromatography, Retention mechanisms, Temperature effects, Thermodynamics,
- Publikační typ
- časopisecké články MeSH
Seven retention models have been selected to describe a dual-retention behavior of ten dopamine-related compounds on polymer-based monolithic stationary phase with zwitterion sulfobetaine functionality. Regression quality, as well as a statistical significance of individual regression parameters, have been evaluated. Better regression performance showed two four-parameter models when compared to three-parameter models. On the other hand, limited number of experimental points disqualified statistical robustness of four-parameter models. Among three-parameter models, retention description introduced by Horváth and Liang provided comparable quality of regression at significantly improved robustness. Multivariate analysis of the best three-parameter models provided the description of physicochemical properties of dopamine precursors and metabolites. Principal component analysis and logistic regression allowed structural characterization of dopamine-related compounds based solely on regression parameters extracted from an isocratic elution data. Both polarity and type of functional groups has been correctly assigned for 3-methoxytyramine that has not been part of an evaluation study. Among applied dual-retention models, Horváth´s model, initially developed to describe a retention of ionic compounds on nonpolar stationary phases, provided robust regression of experimental data and allowed an extraction of structural characteristics of dopamine-related compounds.
- Klíčová slova
- Dopamine, Dual-retention, Polymer monolith, Regression analysis, Retention model,
- MeSH
- betain analogy a deriváty chemie MeSH
- chemické modely * MeSH
- dopamin analogy a deriváty chemie MeSH
- molekulární struktura MeSH
- polymery chemie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- 3-methoxytyramine MeSH Prohlížeč
- betain MeSH
- dopamin MeSH
- polymery MeSH
- sulfobetaine MeSH Prohlížeč
The retention behavior of a large group of analytes (35) with varied properties (pKa and logP) was studied on eight hydrophilic interaction LC columns with different surfaces, stationary phase chemistries, and types of particles. The acetonitrile content (5-95%), buffer concentration (0.5-200 mM), and pH of the mobile phase (3.8 and 6.8) were evaluated for their effects on the retention behavior. The type of stationary phase had a significant impact on the selectivity and retention time of the tested analytes. Completely different selectivity was observed on the aminopropyl stationary phase. In this study, the influence of the buffer concentration was similar for all tested columns, except for the aminopropyl stationary phase. Increasing the buffer concentration led to decreased retention times for the basic compounds and increased retention times for the acidic compounds, while the inverse behavior was observed on the aminopropyl stationary phase. The selectivity of the individual stationary phases was evaluated at pH 3.8 and 6.8. Much lower selectivity differences between the stationary phases were observed at pH 6.8 than pH 3.8. Bare silica stationary phases were used in the comparison of the particles (fused-core and fully porous particles of 3 and 1.7 μm) and the columns provided by different manufacturers.
- Klíčová slova
- Buffer concentration effects, Hydrophilic interaction liquid chromatography, Retention mechanisms, Stationary phases, pH effects,
- MeSH
- chromatografie kapalinová přístrojové vybavení MeSH
- hydrofobní a hydrofilní interakce MeSH
- koncentrace vodíkových iontů MeSH
- organické látky chemie MeSH
- oxid křemičitý chemie MeSH
- poréznost MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- organické látky MeSH
- oxid křemičitý MeSH
The behavior of nanometer or micrometer-sized particles, dispersed in liquid phase and exposed to temperature gradient, is a complex and not yet well understood phenomenon. Thermal field-flow fractionation (TFFF), using conventional-size channels, played an important role in the studies of this phenomenon. In addition to thermal diffusion (thermophoresis) and molecular diffusion or Brownian movement, several secondary effects such as particle-particle and/or particle-wall interactions, chemical equilibria with the components of the carrier liquid, buoyant and lift forces, etc., may contribute to the retention and complicate the understanding of the relations between the thermal diffusion and the characteristics of the retained particles. Microthermal FFF is a new high-performance technique allowing much easier manipulation and control of the operational parameters within an extended range of experimental conditions in comparison with conventional TFFF. Consequently, in combination with various other methods, it is well suited for a detailed investigation of the mentioned effects. In this work, some contradictory published results concerning the thermal diffusion of the colloidal particles, studied by TFFF but also by other methods, are analyzed and compared with our experimental findings.
The total solute retention by a chemically modified stationary phase (CMSP) has been shown several times to be a potential tool for studying the binding abilities of the bound compound. In this article, we present a methodology for the deconvolution of the total retention into structure-specific contributions. Three complementary silica-based CMSPs were prepared: 1) non-modified silica, 2) silica modified by syn-bis-Tröger's base (a molecular tweezer) and 3) silica modified by anti-bis-Tröger's base (a non-tweezer molecule). These were characterized by elemental analysis and Raman spectroscopy, and used to assemble liquid chromatography (LC) columns. The total retention factors were estimated for electron-deficient nitro- and cyano-derivatives of benzene in both normal and reverse elution modes. The total retention factor was considered to be the sum of structure-specific retention factors, each related to the affinity (the binding constant) of a specific structure (the binding site), and its content in the modified silica, as defined for weak-affinity chromatography (WAC). The obtained structure-specific contributions are in line with the binding studies of ligands in solution. They reveal details of the retention mechanism, suggesting a more suitable attachment of ligands, and expose the shortcomings of evaluations based solely on the total retentions.
- Klíčová slova
- binding constant, bound receptor, retention factor, retention mechanism, tweezer effect, weak affinity chromatography,
- MeSH
- chromatografie kapalinová metody MeSH
- ligandy MeSH
- oxid křemičitý chemie MeSH
- roztoky MeSH
- stereoizomerie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- ligandy MeSH
- oxid křemičitý MeSH
- roztoky MeSH
The amount of water adsorbed on polar columns plays important role in hydrophilic interaction liquid chromatography. It may strongly differ for the individual types of polar columns used in this separation mode. We measured adsorption isotherms of water on an amide and three diol-bonded stationary phases that differ in the chemistry of the bonded ligands and properties of the silica gel support. We studied the effects of the adsorbed water on the retention of aromatic carboxylic acids, flavonoids, benzoic acid derivatives, nucleic bases, and nucleosides in aqueous-acetonitrile mobile phases over the full composition range. The graphs of the retention factors versus the volume fraction of water in mobile phase show "U-profile" characteristic of a dual hydrophilic interaction-reversed phase retention mechanism. The minimum on the graph that marks the changing retention mechanism depends on the amount of adsorbed water. The linear solvation energy relationship model suggests that the retention in the hydrophilic interaction liquid chromatography mode is controlled mainly by proton-donor interactions in the stationary phase, depending on the column type. Finally, the accuracy of hydrophilic interaction liquid chromatography gradient prediction improves for columns that show a high water adsorption.
- Klíčová slova
- amide-bonded phases, diol-bonded phases, dual retention mechanism, hydrophilic interaction chromatography, water adsorption on columns,
- Publikační typ
- časopisecké články MeSH
The idea that place navigation in the Morris water maze is implemented by path integration between locations determined by landmark sighting was investigated in a 200-cm-diameter pool in which circular (7.2 degrees/s) motion of water could be induced by tangentially arranged water jets. The rats were trained at 8 trials per day to navigate to an erectable platform which was raised after the rat had spent a criterion time in the target annulus (30 cm in diameter) in the midpoint of the NW quadrant. Asymptotic escape latency of 7 s was reached after 9 days in moving water (n = 8) and after 6 days in stationary water (n = 8). The group overtrained for 13 days in stable water performed well even after it was transferred to moving water. Changing the sense of rotation of water from counterclockwise to clockwise did not affect the asymptotic performance. The above findings show that overtrained rats rely on landmark sighting rather than on path integration. The influence of water movement reappeared when place navigation to a new target (SW) was examined in alternating 2-s periods of light (L) and darkness (D). On the first day, the latencies were 15.2 +/- 1.2 and 22.8 +/- 1.9 s in stable and moving water, respectively, but dropped to 10 s on the following day. The tracks generated in the L period were more tortuous than those generated in the D period and this difference was more pronounced in moving than in stable water. It is concluded that path integration mechanisms supporting navigation during intervals of darkness are impaired in moving water but that this impairment disappears in overtrained animals.
- MeSH
- bludiště - učení * MeSH
- krysa rodu Rattus MeSH
- orientace * MeSH
- plavání MeSH
- pohyb vody MeSH
- pozornost * MeSH
- řešení problému MeSH
- retence (psychologie) MeSH
- rozpomínání * MeSH
- úniková reakce * MeSH
- zvířata MeSH
- Check Tag
- krysa rodu Rattus MeSH
- mužské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The purpose of the present study was to elucidate signaling pathways by which insulin like-growth factor 1 (IGF1) promotes FSH-stimulated synthesis and retention of hyaluronic acid (HA) in pig oocyte-cumulus complexes (OCCs) cultured in serum-free medium. We found that IGF1 had no effects on FSH-stimulated production of cAMP and activation of protein kinase A in the OCCs. Immunoblotting with phospho-specific antibodies showed that FSH moderately phosphorylated v-akt murine thymoma viral oncogene homolog (AKT) and mitogen-activated kinase 3 and 1 (MAPK3/1) in cumulus cells. The exposure of OCCs to both FSH and IGF1 resulted in a significant (P < 0.05) increase in AKT and MAPK3/1 phosphorylation. An inhibitor of phosphoinositide-3-kinase (PIK3), LY 294002, significantly (P < 0.05) reduced the IGF1-enhanced phosphorylation of AKT, and inhibitors of AKT (SH6) and MAPK3/1 (U0126) significantly (P < 0.05) decreased the synthesis and retention of HA stimulated by concomitant exposure of OCCs to both FSH and IGF1. The IGF1-promoted synthesis of HA was not accompanied by an increase in the relative abundance of hyaluronan synthase 2 (HAS2) mRNA in the cumulus cells. We conclude that IGF1 promotes the FSH-stimulated synthesis and retention of HA in pig OCCs by PIK3/AKT- and MAPK3/1-dependent mechanisms.
- MeSH
- AMP cyklický biosyntéza MeSH
- folikulární buňky cytologie účinky léků metabolismus MeSH
- folikuly stimulující hormon farmakologie MeSH
- fosfatidylinositol-3-kinasy metabolismus MeSH
- fosforylace účinky léků MeSH
- glukuronosyltransferasa genetika metabolismus MeSH
- hyaluronansynthasy MeSH
- insulinu podobný růstový faktor I farmakologie MeSH
- kultivované buňky MeSH
- kyselina hyaluronová biosyntéza metabolismus MeSH
- mitogenem aktivovaná proteinkinasa 3 metabolismus MeSH
- oocyty účinky léků metabolismus MeSH
- prasata MeSH
- proliferace buněk účinky léků MeSH
- proteinkinasy závislé na cyklickém AMP metabolismus MeSH
- protoonkogenní proteiny c-akt metabolismus MeSH
- zvířata MeSH
- Check Tag
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- AMP cyklický MeSH
- folikuly stimulující hormon MeSH
- fosfatidylinositol-3-kinasy MeSH
- glukuronosyltransferasa MeSH
- hyaluronansynthasy MeSH
- insulinu podobný růstový faktor I MeSH
- kyselina hyaluronová MeSH
- mitogenem aktivovaná proteinkinasa 3 MeSH
- proteinkinasy závislé na cyklickém AMP MeSH
- protoonkogenní proteiny c-akt MeSH
